Method of making sheet steel



Patented Aug. 12, 1952 METHOD OF MAKING SHEET STEEL Harold L. Farling, Garfield Heights, and Edward C. Norris, Cleveland, Ohio, assignors to Republic Steel Corporation, cleveland flhio, a corporation of New Jersey No Drawing. Application October 19, 1949, Serial N0. 122,358

6 Claims.

The present invention relates generally to the. sheet steel art and more particularly to a new method of making low carbon sheet steel having uniform, good drawing and forming characteristics and havin grains which range in size between about 5 and about 7 in terms of the standards of the American Society for Testing Materials throughout the steel from surface to surface.

For certain purposes sheet and strip steel should have fairly large grains of substantially uniform size throughout the thickness of the steel, 2. minimum amount of resiliency or spring-back, commonly referred to as temper, and low yield points. Such properties are desired in sheet steel which is to be used in making various products by forming or drawing, for example, eave troughs, conductor pipes and allied products. These properties and characteristics have not been obtainable heretofore in sheets or stripsproduced by conventional rolling methods in continuous sheet i or strip mills. These mills, as operated hereto,- fore, produced sheets and strips which had grains ranging in size from about 7 to about 9 in terms of the standards of the American Society for Testing Materials, the smaller grains being in the interior portions and the larger, grains being in the surface portions, and the sheets and strips had a relatively high degree of resiliency or spring-back, and yield points which were higher than was desired in the above mentioned products.

Many efiorts have been made, ever since the continuous sheet or strip mills came into general use, to use those mills to produce sheet and strip steel having the desirable properties and characteristics above mentioned, but so far as we know, none of these efforts by standard or conventional mill processing has been entirely satisfactory.

We have discovered that these desirable properties and characteristics in the finished sheet or strip may be obtained, when simple steel is rolled in a continuous sheet or strip mill, by critically straining the steel in the hot rolling operation. This straining is produced while the steel is at a temperature between about 1600 F. and about 1000 F., preferably between ,1-600 F. and 1420 F., by making successive finishing pass reductions which relatively and percentagewise are medium heavy, light and medium heavy. Steel which has been so strained should be given a small reduction while still in the alpha iron form or magnetic transition range, as in a finishing pass, and may also be reduced in a later pass. It may be continuously pickled, cold rolled to the desired thickness after hot rolling and before being annealed.

, as by being rolled in a light skin or temper pass,

Stand l after being annealed.

The present invention will be better understood by those skilled in the art from the followin illustrative, but not limiting, examples: Slabs of low carbon steel containing about .07 of carbon, about 30% of manganese, about .012% phosphorous, about .033% of sulphur, about .06% nickel, and about 04% copper were heated to a temperature of about 2250" F. in a triple-fired Rust furnace using natural gas as a fuel. These slabs were continuously hot rolled into strips about 31%" wide and about'.070 thick on a continuous hot mill and were coiled without quenching. The hot mill setup was such that the strips entering the finishing stands of the mill were as light as possible consistent with good rolling practice. In a typical instance the six finishing roll stands were so adjusted that the reductions made in the strip were respectively as follows:

2 3 4 5 6 Percentage 50 40 4 6 The light reduction in pass 3 preceded by one or more heavy or medium reductions, such as in pass 2 or 1 and 2, and followed by the medium heavy reduction in pass 4 is important to the present invention. According to prior practice the reductions have decreased in each succeeding finishing stand and have not been medium heavy, light and then medium heavy as is essential to attain the results of this invention.

These hot rolled coiled strips were continuously pickled and cold rolled to the desired final thickness of about .018. These strips were then annealed at a temperature of about 1200 F., after which they were "given alight skin or temper pass to give the steel about a #4 temper and were then cut into sheets of the desired lengths and widths.

Examination of these sheets showed that the size of the grains was between 5 and 8 of the A. S. T. M. grain size standard and that there was substantially no variation in grain size from. surface to surface of the strips. These sheets were readily drawn or formed into products of the type mentioned and had a low degree of resiliency or spring-back and low yield points.

The achievements of the'present invention are indicated by'the following tables which show the contrasts in physical properties and microstructure of steel sheets .018" thick of substantially 'the same compositionwhich were made in the conventional manner with a continuous mill and when they were made by the present invention.

Physical properties and microstructure for comparative purposes on conventional material and material produced according to this invention would conform to the following:

finishing pass, illustrated by pass 4, and following the light pass, illustrated by pass 3, may be from about 38% to about 42%. When the reductions are in the lower end of this range the grains are not as nearly uniform in size from surface to surface of the steel as is the case when reduc- Conoeniional material cold reduced, boa: annealed, temper rolled Yield Point, Ult. Strength, Eloug. in Rockwell in. in. percent Olsen Mierostructure 39, 770 48, 500 51 368 $909+ 38, 540 50, 200 32 53 389 $909+ 38, 690 50, 920 3D 53 374 $909+ 32, 910 46, 470 34 51 391 SQMSCQ 33, 8B0 47, 430 36 51 377 SBMBCQ 38, 490 49, 330 29 54 382 909+ 36, 210 48, 090 23 53 366 SQL'IBCQ 37, 900 50. 350 29 52 383 $909+ 35, 950 47, 930 33 55 364 S9IVI8C9+ 46, 770 34 52 v 387 S B18091- Material produced according 'to our invention Yield Point, Ult. Strength, Elong. in Rockwell a q in. lbJsq in 11 percent Tn OiSL-D. L IiClOStYUCtIlIB 27, 070 44, 220 37 45 376 6-7lu5-8 28, 200 43, 300 i7 354 671\I58 27, 600 44, 800 H 44 '36!) 7M6-8 25, 600 41, 100 41 47 349 6M5-7 28. 600 46, 800 35 47 355 6-7M58 25, 7.60 100 39 11 331 5-6M58 27, 410 4'1, 700 3G 46 344 6L157 25, 600 42,810 36 45 366 7-8 25, 800 43, 200 43 46 375 5-6 29,520 441,300 36 49 368 SM7-8 "It will be noted that the sheets of the first table have yield points which range from 32910 to 39770 and average 36615; and that the grains range from S to 9. In contrast, the sheets of the second table have yield points which range from 25600 to 29520 and average 27316; and grains ranging from 5 to 8. It will also be noted that the elon-,

Carbon 102% -to 15% ltlemganeseuuuh 03% to 15% Phosphorusuu 005% to 05% Sulphur 01% to 08% Silicon u r Residual amounts Copper -Q] Chromed Nickel V L p to 2 7 Molybdenum s Iron s i Remainder The present process may also be used onsimple low carbon steels killed with either aluminum or silicon. In case a steel ofthe foregoing general composition is killed with silicon, the silicon in the killed steel would amount to from about 04% to about 08% if semi-killed, or over .08% if fully killed. Likewise, if killed with aluminum, the aluminum in the killed steel would amount to over ."025%. V

The range :of reductions in the medium heavy tions in the higher part of this range are used, but the grains in the surface portions are between about 5 and about 7 on the A. S. T. M. scale. When the reduction in the medium heavy pass is approximately 40% and follows a reduction of about 35% in the light pass, the size of the grains is uniformly 5 to 7 throughout the steel.

The medium heavy pass reduction taken after the light pass may be taken at temperatures between about 1600 F. and about 1000 F. but preferably is taken between about 1600 F. and about 1420 F. The extent of hot reduction following this medium heavy reduction of the steel may range from about 2% to about 6% with the larger reduction being taken when this medium heavy reduction has been in the lower portion of the 38% to 42% range. About 4% reduction is preferred with this medium heavy reduction of about 40%.

Since continuous hot mills are not usually employed to reduce hot strip to less than about .070" in thickness, for cold reducing purposes, the steel rolled to that thickness by the present process may be subsequently cold rolled to bring it to thinner desired thickness.

The cold rolling reductions in thickness may range from about 15% to about 80%, but preferably range between 30% and "The steel, whether hot rolled only or hot rolled and cold, rolled, is annealed at'temperatures from about l1 75 and about 1380 'F., but preferably at about 1200F.

The annealed steelmay be given the desired degree of temper by being cold rolled, but such rolling is preferably of the light skin pass type fora low degree of temper is preferred with the large grains of the steel resulting from the forens steps.

Steel produced by this invention may be used in the uncoated form or may be coated as by being galvanized, hot dipped or electroplated.

This application is a continuation-in-part of our copending application, Serial No. 627,794, filed November 9, 1945, now abandoned.

Having thus described our invention so that others skilled in the art may be able to understand and practice the same, We state that what we desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of making steel in sheet or strip form which comprises the steps of continuously rolling simple low carbon steel while such steel is in the temperature range of from about 1600 F. to about 1000 F., and reducing its thickness about 40% in a medium heavy reduction finishing pass, then about 35% in a light reduction finishing pass, and then about 40 in a medium heavy reduction pass.

2. The method of making steel in sheet or strip form which comprises the steps of continuously rolling simple low carbon steel while such steel is in the temperature range of from about 1600 F.

to about 1000 F., reducing its thickness about I 40% in a medium heavy reduction finishing pass, then about 35% in a light reduction finishing pass, and then about 40% in a medium heavy reduction finishing pass, and then about 4% and about 6% respectively in the next two succeeding finishing passes.

3. The method of making steel in sheet or strip form which comprises the steps of continuously rolling simple low carbon steel while such steel is in the temperature range of from about 1600 F. to about 1000 F., reducing its thickness about 40% in a medium heavy reduction finishing pass, then about 35% in a light reduction finishing pass, and then about 40% in a medium heavy reduction finishing pass, then about 4% and about 6% respectively in the next two succeeding finishing passes, cold rolling the thus hot rolled steel, and annealing the thus cold rolled steel at a temperature between about 1175 F. and about 1380 F.

4. The method of making steel in sheet or strip form which comprises the steps of continuously rolling simple low carbon steel containing between about .02% and about of carbon, between about .03% and about 0.6% of manganese, between about 005% and about 05% of phosphorous, between about .01% and about .08% of sulphur, residual amounts of silicon, copper, chromium, nickel and molybdenum totaling up to about 0.2%, and the remainder iron, while such steel is in the temperature range of from about 1600 F. to about 1000 F., reducing its thickness about 40% in a medium heavy reduction finishing pass, then about in a light 1'..- duction finishing pass, and then about in a medium heavy reduction finishing pass, cold rolling the thus hot rolled steel, and annealing the thus cold rolled steel at a temperature between about 1175 F. and about 1380 F.

5. The method of making steel in sheet or strip form which comprises the steps of com tinuously rolling simple low carbon steel while such steel is in the temperature range of from about 1600 F. to about 1000 F., reducing its thickness about 40% in a medium heavy reduction finishing pass, then about 35% in a light reduction finishing pass, and then about 40% in a medium heavy reduction finishing pass, pickling the steel, cold rolling the thus hot rolled and pickled steel and reducing its thickness between about 30% and about to bring it to the desired thickness, and annealing the thus cold rolled steel at a temperature between about 1175 F. and about 1380 F.

6. The method of making steel in sheet or strip form which comprises the steps of continuously rolling simple low carbon rimmed steel containing between about .02% and about 15% of carbon, between about .03 and about 0.6% of manganese, between about 005% and about .05% of phosphorous, between about .01% and about 08% of sulphur, residual amounts of silicon, copper, chromium, nickel and molybdenum totaling up to about 0.2% and the remainder iron, While such steel is in the temperature range of from about 1600 F. to about 1000 F., reducing its thickness about 40% in a medium heavy reduction finishing pass, then about 35% in a light reduction finishing pass, and then about 40% in a medium heavy reduction finishing pass, and then about 4% and about 6% respectively in the next two succeeding passes, pickling the steel, cold rolling the thus hot rolled and pickled steel and reducing its thickness between about 30% and about 75% to bring it to the desired thickness, annealing the thus cold rolled steel at a temperature between about 1175 F. and about 1380 F. and thereafter imparting a small degree of temper to the thus annealed steel by subjecting it to a light skin rolling pass.

HAROLD L. FARLING. EDWARD C. NORRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,785,786 Patterson Dec. 23, 1930 1,946,240 Rohn Feb. 6, 1934 2,087,765 Schermer July 20, 1937 2,087,766 Forbes et a1 July 20, 1937 2,125,153 Chace July 26, 1938 2,377,922 Campbell et al. June 12, 1945 2,381,435 Burns et al. Aug. 7, 1945 FOREIGN PATENTS Number Country Date 423,868 Great Britain Feb. 11, 1935 OTHER REFERENCES f Metals Handbook, pages 818-825, 1935 edi- The Making, Shaping and Treating of Steel," Camp and Francis, 6th edition, page 1217, 1940. 

3. THE METHOD OF MAKING STEEL IN SHEET OR STRIP FORM WHICH COMPRISES THE STEPS OF CONTINUOUSLY ROLLING SIMPLE LOW CARBON STEEL WHILE SUCH STEEL IS IN THE TEMPERATURE RANGE OF FROM ABOUT 1600* F. TO ABOUT 1000* F., REDUCING ITS THICKNESS ABOUT 40% IN A MEDIUM HEAVY REDUCTION FINISHING PASS, THEN ABOUT 35% IN A LIGHT REDUCTION FINISHING PASS, AND THEN ABOUT 40% IN A MEDIUM HEAVY REDUCTION FINISHING PASS, THEN ABOUT 4% AND ABOUT 6% RESPECTIVELY IN THE NEXT TWO SUCCEEDING FINISHING PASSES, COLD ROLLING THE THUS HOT ROLLED STEEL, AND ANNEALING THE THUS COLD ROLLED STEEL AT A TEMPERATURE BETWEEN ABOUT 1175* F. AND ABOUT 1380* F. 